ELECTROLYTIC SYNTHESIS OF DIBASIC ACIDS. 365 



The dissociation constant was determined with the following result : — 



o 



Anti-s-diethylsuccinic acid prepared by electrolytic synthesis. 



COOHCH(C 2 H 5 )CH(C 2 H 5 )COOH. 



Mx> =351. 



V 



fJ- 







100m 



K 



937 



58-0 







16-52 



00349 



187-4 



790 







2250 



00349 



374-8 



105-3 







300 



00343 



749-6 



1390 







39-6 



0-0347 



1499 



1772 



K = 



= 0-0347 



50-5 



00347 



Bischoff and Walden # found K = 0"0343. 



Synthesis of Tetramethylsuccinic Acid. 



Ethyl-potassium dimethylmalonate, the substance from which we started in the 

 synthesis of tetramethylsuccinic acid, cannot be prepared from diethyl dimethylmalonate 

 by the method which we used in previous cases. When alcoholic caustic potash, in the 

 calculated quantity, is added to an alcoholic solution of the diethyl ether, either all at 

 once, or slowly, half of the ether is completely saponified, and half of it left quite 

 unattacked, the ethyl-potassium salt being formed only in very small quantity. By 

 modifying the conditions, however, we were able to effect the half-saponification satis- 

 factorily. The points to be attended to are great dilution and low temperature. 



100 grammes of diethyl dimethylmalonate were dissolved in a litre and a half of 

 95 per cent, alcohol, and cooled to 0°. To this was added at once, while the liquid was 

 stirred, 8 grammes of caustic potash (one quarter of the quantity required for half-saponi- 

 fication) dissolved in 200 cc. of alcohol, and also cooled down to 0°. The caustic potash is 

 thus greatly diluted, and the saponification takes place very slowly. The solution was 

 allowed to stand overnight and then boiled, when no separation of the dipotassium salt 

 took place. The alcohol was distilled off on the water-bath, and the residue treated with 

 about 200 cc. of water. The excess of diethyl ether separated as an oily layer, while the 

 ethyl-potassium salt dissolved in the water. The aqueous solution was extracted with ether, 

 the ethereal extract added to the ethereal layer, and, after removal of the ether, the residual 

 diethyl dimethylmalonate subjected to the processes just described. In this way, practi- 

 cally the whole of the diethyl dimethylmalonate was converted into the ethyl-potassium 

 salt. The final aqueous solution contained only traces of the dipotassium salt, and was 

 subjected to electrolysis after evaporation to a suitable strength. 



* Berichteder deutsche chemische Gesellschaft 22, 1821. 



